Fuel injection system for internal combustion engines



Oct. 7, 1969 E|5ELE ET AL 3,470,854

FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES Filed Oct. 24, 19 67 2 Sheets-Sheet 1 INVENTORS Hermann EISELE Frledmch RABUS Walter RIMA ZKI their ATTORNEY Oct. 7, 1969 E L ETAL 3,470,854

FUEL INJECTION SYSTEM FOR INTERNAL COMBUSTION ENGINES Filed Oct. 24. 1967 2 Sheets-Sheet 2 INVENTORS Hermann EISELE Friedrich RABUS Walter RIMATZKI their ATTORNEY United States Patent Ofice 3,470,854 Patented Oct. 7,, 1969 B 89,6 Int. Cl. F02m 37/08; F02d 33/00 US. Cl. 123-32 9 Claims ABSTRACT OF THE DISCLOSURE Pulses having a recurrence rate depending on engine speed, and controlling the opening time of electromagnetic fuel injection valves, are applied to a timing circuit which operates a relay interrupting power to the fuel supply pump when engine speed falls below a given value to prevent low speed flooding of the engine upon malfunction of the fuel injection valves.

The present invention relates to a fuel injection system for internal combustion engines and more particularly, to such a system in which electromagnetically controlled valves are opened under control of an electronic control arrangement in synchronism with the speed of the engine to inject fuel supplied to the valves by an electrically driven fuel pump.

Fuel injection systems customarily are arranged such that connection of the fuel injection system also connects the fuel supply pump. When the internal combustion engine, and its fuel injection system are new, satisfactory operation is usually obtained. If, however, any one of the injection valves become defective, so that the valves do not close tightly any more, or if, due to a malfunction of the valves or the electronic control, a valve remains open constantly, then the fuel supply pump will pump fuel into the respective cylinder Without interruption. If the internal combustion engine is standing still, or running only very slowly, then the excess fuel cannot be removed from the cylinder, which will flood, and the engine will stall.

It is an object of the present invention to prevent stalling of internal combustion engines having a fuel injection system even if the valves should not function perfectly.

Subject matter of the present invention Briefly, in accordance with the present invention, a control circuit is provided for the fuel pump, the action of which depends upon speed of the engine, and which interrupts the current supply to the fuel pump when the speed of the engine drops below a certain minimum value. The minimum speed value at which interruption of the fuel pump occurs is set to be less than the idling speed, so that the flooding of one or more cylinders of the internal combustion engine can be avoided.

It is necessary that the fuel supply operates when it is intended to start the engine, even though the engine may still be motionless, or be turning over very slowly. According to a feature of the present invention, the starting switch provides for application of electrical current to the fuel supply pump independently of the speed of the engine.

According to a further feature of the invention, a first monostable multivibrator circuit is synchronized with the speed of the engine, supplying pulses to a timing circuit; the potential across the timing circuit then controls a transistor switch which, in turn, controls the current supply to the fuel injecion valves. A very simple circuit can thus be provided. The potential across the timing circuit, as applied by the pulses from the first multivibrator, can be made to depend not only on the speed of the engine but also on operating parameters, such as the vacuum in the intake manifold, temperature and the like. If the speed at which the pump is disconnected is to be always the same, then preferably a second multivibrator is provided, applying output pulses in synchronism with the speed of the engine, which are likewise applied to the timing circuit. The potential across the timing circuit will then become a function of the speed only. In many cases, a second multivibrator may already be available in the fuel injection control system, and it can be utilized in the circuit of the present invention. A simple construction of the timing circiut is obtained if the second multivibrator provides rather long impulses.

The structure, organization, and operation of the invention will now be described more specifically with reference to the accompanying drawings, wherein:

FIG. 1 is a partly schematic, partly circuit diagram of a fuel injection system; and

FIG. 2 is a schematic and block diagram of another embodiment of the present invention.

FIGURE 1 illustrates a fuel injection system for use with a four cylinder engine 10, having spark plugs 11 connected to an ignition system not shown. The inlet manifold 12 has individual intake stubs leading to the cylinders of engine 10. Electromagnetically operated injection valves 13 are located on the inlet stubs immediately adjacent the inlet valves of the engine. The four injection valves 13 together form the injection system for engine 10. Fuel is applied to the injection valves 13 over fuel lines 14 from a distributor 15. A pump 16 supplies fuel from a fuel tank 17 to the distributor 15 and maintains the fuel therein under substantially constant pressure, for example, by means of an over pressure valve, or by a pressure regulator throttle in a return line (not shown) and as known in the art.

Pump 16 is driven by an electric motor 18 which can be switched ON over a contact r of a relay R. The current through the coil of Relay R is controlled by a circuit 23, containing a pair of npn transistors 21, 22, which, in turn, are controlled from the output of a timing circuit 24. Output pulses of a first monostable multivibrator 25 are applied to timing circuit 24. The monostable multivibrator 25 has a pair of pnp transistors 26, 27, the output impulses of which are applied over an amplifier 28 and a transfer switch 29 to a pair of output power transistors 32, 33. The collectors of transistors 32, 33 are connected over resistances 30, 31 to two injection valves 13, respectively. The other terminals of the injection valves are connected to the chassis. Amplifier 28 and transistors 32 and 33 together form a power stage 30 as indicated by the dot-dashed lines in FIGURE 1.

To control the duration of the output pulses appearing at the collector of transistor 27, multivibrator 25 includes a timing circuit formed by the primary 40 of a transducer 39 inserted in the collector circuit of transistor 27, and the combination of resistances 61, 66. The inductivity of winding 40 is made dependent on the vac uum in the intake manifold 12, so that the impulse period, and thus the fuel injected into each cylinder is a function of the vacuum. Transducer 39 has a movable core 41, connected by means of a linkage schematically indicated by dashed line 42 with a vacuum chamber 43 connected to the intake manifold 12. A throttle 46, controlled by the fuel controller, or gas pedal 45 controls the vacuum within intake manifold 12; if the vacuum in the intake manifold increases, linkage 42 is shifted upwardly in the direction of the arrow, shifting the position of the ing the inductivity of winding 40. If, conversely,throttle 46 is opened the inductivity of winding 40 increases.

Transducer 39 is formed with a secondary winding 47 having one terminal connected to the base of transistor 26 and the other to the junction point of a voltage divider formed of resistances 48, 49 and connected across a pair of lines 50, 51 connected to a source of current supply, for example, a 12-volt battery. Lines 50, 51 form the positive and negative buses of the system respectively. Negative bus 51 is connected to chassis as shown.

The emitters of transistors 26, 27 are connected direct- 1y to the positive bus 50. The collector of transistor 26 is connected over a coupling resistance 52 with the base of transistor 27, and over a collector resistance 53 with negative bus 51. A resistance 54 connects the base of transistor 27 to positive bus 50. The output impulses of multivibrator 25 are synchronized with the speed of the engine 10. A cam 56, having a pair of rises, closes a movable switch-arm 57 against a fixed terminal 58 twice during each rotation of the camshaft of engine 10. Contact 58 is connected over a condenser 59 with the base of transistor 26 and over a resistance 60 with the positive bus 50. The positive pulses occurring during opening of switch-arm 57 are applied to the previously conductive transistor 26, so that transistor 26 blocks, and transistor 27 begins to become conductive, causing current to fiow through primary winding 40 of transducer 39. The current through the primary winding 40 increases exponentially with a time constant which depends on the inductivity of the primary winding 40. The maximum value of the current is determined by the resistance of winding 40 and the series-connected resistance 61.

As this current increases exponentially, a potential is induced in secondary winding 47 which decreases exponentially and maintains the base of transistor 26 positive, so that transistor 26 remains blocked. As soon as this potential has decreased to a value which is less than the potential at the tap point of voltage divider 48, 49, the base of transistor 26 again becomes negative, transistor 26 becomes conductive and blocks transistor 27.

During each opening of the switch-arm 57, a positive pulse occurs at the transistor 27 which is applied by means of transfer switch 29 either to the power transistor 32 or to power transistor 33, thus causing injection of fuel to the respective cylinder pairs. Amplifier 28 amplifies the pulses and further causes inversion of the polarity of the pulses applied to the transistors 32, 33.

At low temperatures it is desirable to inject a greater quantity of fuel, and thus to have a longer impulse. A temperature sensitive resistance in the form of a negative temperature coelficient resistance 67 is connected in series with a temperature stable resistance 66 across buses 50, 51, forming a voltage divider having a temperature-variable tap point S. The cathode of a rectifier 65 connects to tap point S, the anode of which is connected to the junction between winding 40 and resistance 61. Temperature sensitive resistance 67 is mounted in heat conductive relation to the engine. At low temperatures of engine 10, the resistance value is high so that the cathode of the diode 65 is more negative than its anode and a compensating current is permitted to flow which increases the impulse period and thus the injection period during which valves 13 will be open.

The anode of a diode 70 is further connected to the collector of transistor 27; the cathode of diode 70 connects over a resistance 71, with a condenser 72 in parallel, to the negative bus 51, and further to the base of a transistor 22. The collector of transistor 22 is connected with positive bus 50 and the emitter over a resistance 73 with a base of atransistor 21. The emitter of transistor 21 is connected directly to negative bus 51.

The coil of relay R is connected between the collector of transistor 21 and positive bus 50. A quench diode 74 is connected in parallel to the coil of relay R. The base of transistor 21 is connected directly to the cathode of a diode 75 and over a resistance 76 to negative bus 51. The anode of diode 75 connects to a junction 77 which, on the one hand, is connected over a resistance 78 to negative bus 51 and, on the other, to a resistance 79 and to a switch 80, in series therewith, which is ganged with the starter switch of the'i'nternal combustion engine. The other terminal of switch 80 connects to positive bus 50. I

.fLetQit be assumed that starter switch 80. is open, as 511 mm FIGURE 1, andthat the internal combustion engine 10 operates at a speed of, for example, 2,000 r,.p.m. The multivibrator 25 then supplies 2,000 positive pulses per minute, which are applied overdiode 70 to condenser 72. Condenser 72 will be charged during'the pulses and discharged partially during the periods between pulses over resistance 71. A potential will therefore build up across condenser 72 which will maintain transistor 22 conductive; conduction of transistor 22 will maintain transistor 21 conductive, so that current will flow through relay R, maintaining contact r closed. Motor 18 driving fuel pump 16 will thus be operating and fuel can be supplied under pressure to distributor 15 and thence to the injection valves 13. If the speed of the engine 10 falls below a certain minimum value, which can be determined by adjustment of the resistance 71, for example, to 30 r.p.m., the potential on condenser 72 will be so small that transistor 22, and with it transistor 21, will be switched off, causing the relay eontactrto dropout and interrupting current to motor 18 and thus stopping pump 16. No more fuel will be supplied to the injection valves and flooding of one or more of the cylinders of the engine 10 with fuel is thus effectively prevented, even if one of the injection valves should be defective or, after long operating time, does not close tightly anymore. 9

Upon starting, starting switch 80 will be closed. Thus, transistor 21 will receive base current over resistance 79 and diode 75 and becomes conductive, causing the relay contact r to pull in, connecting motor 18 and thus driving pump 16.

FIGURE 2 illustrates a further embodiment of the present invention, and similar parts are referred to with the same reference numerals as in FIGURE 1 but are not described again. In the embodiment of FIGURE 2, a second monostable multivibrator 82 is provided, controlled to deliver pulses in synchronism with the speed of engine 10. Its output pulses have a constant duration and are applied to a timing circuit 24 which controls the circuit 23 as in FIGURE. 1, and thus operation of the relay R. The multivibrator 82 can be operated directly from the impulse source formed by cam 56 and contacts 57, 58; alternatively, it can be driven from the output pulses of multivibrator 25, as shown in FIGURE 2. If the fuel injection system already has a second multivibrator for some other purpose, the pulses from that second multivibrator can be utilized to turn off the fuel supply pump. The arrangement in accordance with FIGURE 2, of course, should also be provided with a circuit coupled to the starter switch in order to start the fuel supply pump motor 18 upon starting of the engine.

By suitable reversal of polarity, transistors of opposite conductivity type can be used.

We claim: 7

1. Fuel injection system for internal combustion engines having electrically controlled fuel injection means and an electrically driven fuel pump comprising: j 0

signal generator means sensing rotational speed of said engine and providing a speed signal therefrom representative of said engine speed; a monostable multi-vibrator responsive to saidspeed signal and changing state in synchronism with the speed of the engine; a timing circuit; 7 means deriving switching pulses from said multi-vibrator and applying said pulses to said timing circuit to place said timing circuit in a condition representative of switching rate;

and a fuel pump control circuit connected to said timing circuit and responsive to the condition thereof, said fuel pump control circuit interrupting operating power to said fuel pump when said speed signal is below a predetermined value.

2. System as claimed in claim 1, wherein:

said pump control circuit includes a transistor switch and said timing circuit includes a charging condenser, the switching state of said transistor switch being controlled by the potential appearing at said charging condenser.

3. System as claimed in claim 2, including a starter switch, and circuit means interconnecting said starter switch and said transistor switch, controlling the switching state of said transistor witch independently of the potential at said charging condenser.

4. System as claimed in claim 2, including a second monostable multivibrator circuit controlled to change state in synchronism with engine speed; and means applying the output pulses of said second monostable multivibrator to said timing circuit.

5. System as claimed in claim 1 wherein said electronic control circuit includes a monostable multivibrator circuit having a constant switching pulse duration and connected to be responsive to said speed signal and controlled to change state in synchronism with engine speed, the switching pulses being applied to said timing circuit, said pump control circuit interrupting current supply to said fuel pump as determined by the potential on said timing circuit.

6. System as claimed in claim 5, wherein said timing circuit includes an RC network, the pulses being applied to said timing circuit to charge the condenser thereof,

and said condenser discharging in the period between pulses applied thereacross, whereby the potential across said condenser will be a function of the speed of the engme.

7. System as claimed in claim 2, wherein said timing circuit includes an R-C network, the pulses being applied to said timing circuit to charge the condenser thereof, and said condenser discharging in the period between pulses applied thereacross, whereby the potential across said condenser will be a function of the speed of the engine.

8. System according to claim 1, including an additional monostable multivibrator circuit, said additional multivibrator circuit having a fixed switching pulse duration, and being connected to change state upon change of state of said monostable multivibrator and applying its output pulses to said timing circuit.

9. System according to claim 8, wherein said timing circuit includes an R-C network, the pulses being applied to said timing circuit to charge the condenser thereof, and said condenser discharging in the period between pulses applied thereacross, whereby the potential across said condenser will be a function of the speed of the engine.

References Cited UNITED STATES PATENTS 2,912,595 11/1959 Kehm et al. 3,053,243 9/ 1962 Domann. 3,272,187 9/ 1966 Westbrook et al. 2,989,644 6/1961 Schultz 123-179 XR LAURENCE M. GOODRIDGE, Primary Examiner US. Cl. X.R. 123-139, 179 

